Moisture Performance of Closed Crawlspaces

Moisture Performance of Closed
Crawlspaces and their Impact on
Home Cooling and Heating Energy
in the Southeastern U.S.
Bruce Davis
Cyrus Dastur
ABSTRACT
This study compared the performance of closed crawlspaces, which had sealed foundation wall vents, a sealed polyethylene
film liner, and 1.0 ft3/min (0.5 L/s) of HVAC supply air for each 30 ft2 (2.8 m2) of crawlspace ground surface, to traditional vented
crawlspaces with wall vents and polyethylene film covering 100% of the ground surface. The study was conducted at 12 owneroccupied, all-electric, single-family detached houses with the same floor plan located on one cul-de-sac in the southeastern United
States. Using the matched pairs approach, the houses were divided into three study groups of four houses each. Comparative moisture measurements for these crawlspaces and submetered heat pump kWh use were recorded. Findings supported that for the
humid conditions of the southeastern United States, properly closed crawlspaces were a robust measure that produced substantially drier crawlspaces and significantly reduced occupied space conditioning energy use on an annual basis.
INTRODUCTION
Wall-vented crawlspaces are widely used in building
construction throughout North America. They are cheap to
build, functional in terms of providing a level foundation for
flooring on sloping sites, and popular as spaces in which to
locate plumbing, ductwork, and heating and air-conditioning
systems. Crawlspaces can be a source of a host of moisture
problems. The crawlspace project is a multi-year effort focused
on improving the moisture and energy performance of crawlspace systems. Of particular interest are crawlspaces built in the
humid southeastern United States and other locations with similar climates.
We are not the first to investigate the moisture performance
of wall-vented crawlspaces. Rose (1994) wrote a review of
crawlspace investigation and regulation through history. Rose
and TenWolde (1994) wrote a summary paper to review many
of the issues associated with wall-vented crawlspace construction. The above material, along with that of several others, is
included in Recommended Practices for Controlling Moisture
in Crawl Spaces.1 Additionally, during the first year of this
study, in 2001, Rose contributed an update of the historical
review of crawlspace regulation as part of a technology assessment report (Davis et al. 2002). These articles reference a wide
range of the authors and activities over the years that built the
understanding of wall-vented crawlspace moisture problems
and solutions.
A goal of this research was to demonstrate practical, easily
transferable, and clearly understandable dry crawlspace
construction techniques that would, in addition to solving a
multitude of moisture problems, be at least energy neutral and
at best would reduce energy consumption for occupied space
conditioning.
Current building codes generally enforce the use of foundation wall vents to provide for air exchange between the crawlspace and outside. The intention of these requirements has been
to provide a drying mechanism for these spaces. However,
applying a psychrometric chart to southeastern summer outdoor
air and crawlspace air demonstrated that the moisture load of
1.
Recommended Practices for Controlling Moisture in Crawl
Spaces, ASHRAE Technical Data Bulletin, volume 10, number 3;
available for download only at <www.ashrae.org> (in Bookstore,
Out-of-Print Books).
Bruce Davis is research director and Cyrus Dastur is a research associate with Buildings Group, Advanced Energy, Raleigh, NC.
©2004 ASHRAE.
outdoor air often exceeded that of crawlspace air. The result has
been that crawlspaces became wetter rather than drier from the
exchange of air.
During the humid season, for crawlspace houses located in
the southeastern United States, it has been common experience
within the building industry to find mold growing on crawlspace
framing, moisture beads in floor batt insulation, and condensation forming on truss plates as well as on air-conditioning equipment and ducts. Builders, HVAC contractors, and insulation
contractors have received complaints because of these moisture
conditions. Additionally, hardwood floor installation companies have been asked to correct floors that cup or buckle following move-in and use of air conditioning.
To address these and other widely divergent building moisture issues, the crawlspace project was set up to investigate the
hypothesis that properly closed crawlspaces are a robust
measure that could reduce the incidence of this family of problems that are related to crawlspace moisture. A second hypothesis is that these closed crawlspace construction methods would
not increase and could potentially decrease the energy necessary to provide for space conditioning.
THE RESEARCH
Experiment Design
This paper reports on a study that was conducted at 12 identical, owner-occupied, all-electric single-family detached
houses located on one cul-de-sac, six on each side of the street,
in the southeastern United States. The 1040 ft2 (97 m2) houses
were newly constructed on traditional wall-vented crawlspaces.
Shortly before move-in during the spring of 2001, homeowners
of all 12 houses agreed to participate in the study. Using the
matched pairs approach, the houses were divided into three
groups of four houses each. Additionally, the study design
included two different phases.
The houses were all built on controlled fill soil, which
added to the uniformity of the site. All houses had a series of
building and duct air leakage performance measurements to
confirm similarity of construction tightness. Given that the
houses were substantially airtight, an outside air intake duct
with integrated filter was installed for each heat pump system.
This system provided 40 ft3/min (19 L/s) of outside air into the
house when the heat pump conditioning the house was operating.
Phase One, June 2001 Through May 2003
The three crawlspace groups were: control, experiment
one, and experiment two. The control group had wall foundation vents and 100% of the ground surface was covered with 6mil polyethylene film. The seams were overlapped 6 in. (15 cm)
but were not sealed. The polyethylene film was held in place
with turf staples. Although the building code allowed a reduction in the amount of wall venting when a vapor-retarding
ground cover (VRGC) was present, all eleven, 8 × 16 in. (20 ×
41 cm) foundation vents were retained. The floor was insulated
2
with well-installed, R-19 fiberglass batt insulation placed
between the joists with vapor retarder up. No liquid water was
allowed to enter the crawlspace.
The first experiment group had the wall foundation vents
blocked and sealed from the inside with foam plugs and mastic.
The ground and walls were covered with a continuous, sealed
liner system of 6-mil polyethylene film that was also sealed to
the interior piers and to the foundation wall near the top. The top
3 in. (7.6 cm) of the foundation was not covered with the liner
but was painted with white mastic. This provided a gap for
termite inspection. Foundation penetrations and cracks were
sealed to reduce air infiltration. The floor insulation was
removed and no foundation wall insulation was added, thus
producing closed but uninsulated crawlspaces.
The second experiment group was modified to be the same
as the experiment one group but had the addition of approximately R-3 rockwool insulation blown onto the foundation wall
liner membrane and band joist. The 3 in. (7.6 cm) gap for termite
inspection was retained.
Duct air leakage was measured for all 12 houses. Duct
repair was primarily limited to items that would ensure that the
ducts would not become disconnected during the study. There
were two exceptions. One system needed two duct runs
replaced because of a plumbing leak at move-in. The other
system was repaired to correct a substantial return duct air leak.
That repair brought its duct air leakage in line with the rate of
duct air leakage of the other houses. This measured duct air
leakage was retained throughout Phase I of the study.
Phase Two, June 2003 Through March 2004
Air sealing work was applied to all 12 houses during April
and May 2003. This involved sealing all the floor penetrations
and substantially sealing the existing duct air leakage. R-19
fiberglass batts, vapor retarder up, were added between the floor
joists to the experiment one group, which previously had no
insulation, and in experiment two houses, the rockwool wall
insulation was replaced with 2 in. (5 cm) of R-13 foam insulation. Please note that the termite view strip was retained and that
the wall insulation was not installed in the typically recommended form that specifies wall insulation should be continuous from the subfloor to 24 in. (61 cm) below outside grade or
horizontally on the soil in from the foundation wall for 24 in.
(61 cm). All 12 houses received the same battery of pre- and
post-air leakage measurements that they received at the beginning of the study. In addition, both experiment one and experiment two crawlspaces were fitted with an HVAC supply air duct
that was adjusted to deliver 35 cfm, or 1 ft3/min (0.5 L/s), of
supply air per 30 ft2 (2.8 m2) of crawlspace ground surface. This
supply air was delivered whenever the thermostat called for the
heat pump to condition the living space of the house. To prohibit
passive airflow between the crawlspace and the heat pump duct
system, the crawlspace supply was fitted with a passive backflow damper that remained closed when the heat pump was off
and only opened when the heat pump was running. Each heat
pump was fitted with a standard utility electric meter so that
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kWh use could be recorded each month. All houses retained the
outside air duct that provided 40 ft3/min (19 L/s) of filtered,
outside air to the house when the heat pump was on.
Measurement
To record outside air temperature and moisture content,
three battery-operated data loggers were placed in protected
locations at the experimental site. The same type of data logger
was used for recording conditions inside each house and inside
each crawlspace. Data were recorded every 15 minutes. One
data logger was placed in the center of the house at the return
grille, and two loggers (for redundancy) were located together
in the center of the crawlspace on the support beam for the floor
joists. These loggers were designed to operate from –22°F to
122°F (–30°C to 50°C) and from 0 to 100% relative humidity
[RH]. The RH sensor was designed to withstand intermittent
condensing environments up to 86°F (30°C) and noncondensing environments above 86°F (30°C). In the high resolution
mode, temperature accuracy equaled ±0.33°F at 70°F (±0.2°C
at 21°C). RH accuracy equaled ±3% from 32°F to 122°F (0°C
to 50°C) and ±4% in condensing environments. As mentioned
above, each heat pump was submetered with a standard utility
kWh meter to track occupied space conditioning energy. The
total house kWh was recorded from the utility customer account
meter. Readings were taken from both meters at each house
once per month. The submeters were calibrated to ±0.2% accuracy under both light- and full-load conditions, and readings
were rounded to units of whole kWh. Wood moisture content
readings were taken manually at several dedicated locations in
the crawlspace during specific site visits. The pin wood moisture meter readings were adjusted for both temperature and
species. The wood moisture content meter had an accuracy of
±0.5% for the 6% to 12% range, ±1.0% for the 12% to 20%
range, and ±2% for the 20% to 30% range. The noncontact
temperature meter was designed to provide an accuracy of ±1%
of reading or ±2°F (±1°C), whichever was greater, for ambient
operating temperature from 73°F to 77°F (23°C to 25°C). For
ambient temperatures between 0°F and 73°F (–18°C to 23°C)
the accuracy was rated at ±3°F (±2°C).
While the study generated many other data sets, this article’s focus on crawlspace moisture and occupied space conditioning energy use are depicted in Figures 1 through 9. In several
of the figures, the data for experiment one and experiment two
houses were so similar that they were combined under the title
“closed” for closed crawlspaces. The 15-minute raw data were
averaged to provide one plot point for each 24-hour period. For
Figures 1 through 6, the graphed lines were generated using a
seven-day rolling average to depict the general trends in the
data.
Findings
Figures 1 and 2 graph relative humidity in the crawlspaces
for both Phase I and II. They show that for the critical summer
months the relative humidity in the closed crawlspaces
remained substantially lower than in the wall-vented crawlBuildings IX
spaces. This is especially significant for the Figure 2, Phase II
graph because the summer of 2003 was one of the wettest on
record for the test location and the closed crawlspaces still
remained dry. For the summer seasons, air in the closed crawlspaces was generally below 60% relative humidity and air in the
wall-vented crawlspaces was often above 80% relative humidity. For Figure 1, the June 2001 period reflects two start-up
activities for the study. First, the relative humidity for the closed
crawlspaces was as high as that for the vented crawlspaces. This
is the point in time that the experiment one and experiment two
crawlspaces were closed. Second, a couple of weeks later the
closed crawlspaces dropped to 40% relative humidity. This
represents the brief period of time during which we experimented with using small dehumidifiers as a supplemental
drying mechanism. The dehumidifiers were then disconnected
and the closed crawlspaces stabilized between 55% and 60%
relative humidity with the measured duct air leakage as the
supplemental drying mechanism. The transition of the crawlspaces from Phase I to Phase II took place during April and May
2003 and required that the closed crawlspaces be open for an
extended period of time. The transition is reflected in the rise in
relative humidity shown in Figure 1. In Figure 2, for June 2003,
it can be seen that the transition work was completed and the
crawlspaces were again closed and began to dry. With the opening and adjustment of the HVAC supply air duct, the necessary
supplemental drying mechanism was achieved (1 ft3/min
[0.5 L/s] of supply air per 30 ft2 [2.8 m2] of crawlspace ground
surface). For the air temperatures measured during these
summer periods, high relative humidity was associated with
increased wood moisture content and with mold growth in the
vented crawlspaces.
Figures 3 and 5 graph the crawlspace dew-point temperatures for both Phase I and Phase II. The data for the closed crawlspaces show the drier characteristic when the summer season is
examined. Figure 3 graphs summer data for 2001 and 2002,
which again shows the difference in moisture between closed
and wall-vented crawlspaces. Both 2001 and 2002 had slightly
lower dew-point temperatures than did the 2003 data. Outside
air dew-point temperatures for Phases I and II are shown in
Figures 4 and 6 as references and show the moisture load potential that would impact the crawlspace conditions if outside air
had entered a crawlspace. Figure 5 shows that the dew-point
temperature of the air in the closed crawlspaces for much of the
summer of 2003 stayed below 60°F (16°C), while that in the
wall-vented crawlspaces stayed above 70°F (21°C).
For Phase II, wood moisture content averages for a dedicated sample of floor joists in the three study groups is represented in Figure 7. Wood moisture content for the wall-vented
crawlspaces had a large range from the end-of-summer high of
above 15% to a low of around 9.0%. Joists in the two experiment
groups retained more stable wood moisture content from a high
of around 11% to a low of around 9.5% to 10%.
Figure 8 is provided to more clearly show the potential for
outside air to increase the moisture content of a wall-vented
crawlspace during the summer 2003 Phase II period. The
3
Figure 1 Relative humidity in the crawlspaces, Phase I.
Figure 2 Relative humidity in the crawlspaces, Phase II.
4
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Figure 3 Crawlspace dew-point temperatures for Phase I.
Figure 4 Outside air dew-point temperatures for Phase I.
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5
Figure 5 Crawlspace dew-point temperatures for Phase II.
Figure 6 Outside air dew-point temperatures for Phase II.
6
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Figure 7 Wood moisture content averages for a dedicated sample of floor joists in the three study groups, Phase II.
Figure 8 The potential for outside air to increase the moisture content of a wall-vented crawlspace during summer 2003,
Phase II.
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7
Figure 9 The average energy used for occupied space conditioning for a house in each of the three study groups for each
month since the beginning of Phase II in June 2003.
outside air dew-point temperature is the average value for the
three outside data loggers. The crawlspace temperature is the
average value for the four wall-vented crawlspaces. This graph
is the 15-minute data points plotted over a 48-hour period. If
outside air entered the wall-vented crawlspaces, as is the design
intention, it would encounter surfaces at or below its dew point
for a majority of this time, resulting in condensation. These
conditions occur repeatedly throughout the summer season.
Such condensation on wood framing is absorbed and is likely to
be slow to reevaporate and provides a microclimate to support
mold growth.
Figure 9 represents the average energy used for occupied
space conditioning for a house in each of the three study groups
for each month since the beginning of Phase II in June 2003. We
had been advised when we were beginning this study that we
should not expect to measure any space conditioning energy
savings during the summer season from our experiment modifications. However, when we analyzed utility billing records for
the first year, we realized that there could be notable energy
savings.With the installation of the submeters on the heat pumps
for Phase II, we recorded the different space conditioning
energy use patterns for the three different study groups for the
different seasons. For the 10 months displayed, the closed,
floor-insulated houses (experiment one) have each used an average of 15.3% less energy, 772 kWh ($77), for space conditioning than the vented houses (control). The closed, wall-insulated
houses (experiment two) have each used an average of 15.7%
less energy, 795 kWh ($80), than the controls.
The experiment one houses did not save as much as the
experiment two houses during the summer, but they did outperform them during the winter. However, both experiment groups
8
used less energy for space conditioning than the wall-vented
crawlspace group. The energy use data have not been normalized for indoor thermostat setting. While we did not attempt to
control homeowner thermostat setpoint selection, an examination of the indoor temperature data found that each of the three
groups as a whole were within one to two degrees Fahrenheit of
each other throughout all seasons.
DISCUSSION
Phase I of this study demonstrated that a measured amount
of duct air leakage would provide crawlspace moisture vapor
control. However, we are not advocating duct leakage as a standard moisture vapor control strategy. For a temporary, threeweek period during Phase I, the study also demonstrated that
small dehumidifiers would easily provide control for crawlspace relative humidity. The relative humidity was reduced to
40% during that period. Phase II demonstrated that a measured
amount of HVAC supply air (1 ft3/min [0.5 L/s] for each 30 ft2
[2.8 m2] of crawlspace ground surface) would also provide the
necessary supplemental moisture vapor control.
Well-constructed, extensively wall-vented crawlspaces
without water intrusion and with a 100% vapor retarder ground
cover may prevent wood rot in crawlspaces. For these houses,
the wood moisture content in the vented crawlspaces did rise but
did not reach 19% during the summers studied. This crawlspace
configuration did not, however, prevent moisture condensation
and surface mold growth in these same crawlspaces. It is these
additional conditions, plus the energy savings, that tilt the
balance toward the construction of new or the retrofit of existing
crawlspaces that are properly closed. Crawlspaces with reduced
wall vent area as allowed by code were not examined in this
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study and it is not known whether that configuration would
perform as well as the wall-vented crawlspaces in this control
group.
The minimum goal of this study was to have the experiment modifications result in comparable space conditioning
energy consumption relative to the controls. However, both
experiment house groups actually reduced energy consumption
by 15% relative to conventional crawlspace construction. The
closed, wall-insulated (experiment two) houses performed best
during the summer. The closed, floor-insulated (experiment
one) houses performed best during the winter. The magnitude of
the impact of this research for national energy policy is important. What these levels of energy savings could mean for crawlspace houses in the United States has not yet been calculated,
but it would be significant. In addition to the potential annual
energy savings, there are the added benefits of preventing
several common moisture problems, which, in turn, reduce the
rate of deterioration of structures and the costs of those associated repairs. Pleasantly (and fortunately!), the construction
solution that provides these benefits is a practical, straightforward measure.
When the choice is made to place insulation on the foundation wall for a closed crawlspace, current code requires that
the insulation be continuous from the subfloor down to 24 in.
(61 cm) below outside grade or to turn the insulation in and lay
it on the ground to achieve the equivalent of that 24 in. (61 cm)
of insulation. This is referred to as the “L-shaped” installation
of insulation. This method of installation is not viable for two
reasons. First, there are the multiple stakeholders in crawlspace
construction whose positions will need to be accommodated.
For example, the pest management industry desires an inspection gap at the top of the masonry foundation wall. We provided
a 3 in. (7.6 cm) gap or insulation void. Second, there is also the
need for construction practicality when changing crawlspace
construction techniques. With regard to the L-shaped installation, there are no practical materials at this point in time that
would not interfere with access, inspections, real life construction sequences, and potential pest treatments. Our energy
savings were achieved without continuous insulation and without the L-shaped application. The wall insulation was installed
to a depth of only about 3 in. (7.6 cm) below outside soil grade.
Had the inside soil level been deeper relative to outside soil
level, the insulation would have been installed farther below
outside soil grade.
A final caution is appropriate. The findings of this study
would transfer well to houses with similar geometry and geography as the study homes. However, additional consideration
and study are required for houses in other locations and with
different geometry. Given the matched pair experiment design,
there should be considerable transfer of results for both moisture control and energy savings. But we will not know how well
the moisture and energy performance will transfer to production
houses in other climates until a number are actually constructed.
Explanation of these energy performance results includes the
influence in closed crawlspaces of the soil temperature, the
change in building air leakage patterns, and the reduction in
Buildings IX
building moisture load. Another portion of this study will try to
predict results ahead of time. A hygrothermal model is being
tested against the actual performance of two of these study
houses. Once the model is calibrated, it will be used to project
performance for a number of construction types in different
climates.
The dry crawlspace construction techniques employed in
this study should provide for long-term success. The supplemental drying mechanism was provided by the house space
conditioning equipment. Homeowners would be motivated to
repair the system should it malfunction and thus will maintain
the crawlspace drying function. The airflow damper was manually set and should not require additional adjustment. The backflow damper on the HVAC supply air to the crawlspace was a
simple gravity model with a nonmetallic hinge. The liner material is reasonably durable and repairable, and there are more
durable materials available for areas with heavy use. The
outside ventilation air brought in by the heat pump return duct
more than made up for the airflow to the crawlspace. Air that
would normally flow out of the house because of the outside air
intake was used to dry the crawlspace. The homeowner was
provided with a remote sensing temperature and relative humidity meter so that they would be able to be informed if the crawlspace relative humidity were to rise. It is always the case that
homeowner behaviors can overwhelm any building or equipment system. For the system to maintain its performance, the
homeowner must change air filters, provide basic home and
equipment maintenance over time, and observe the meter reading and react as necessary. On the construction industry side,
there are always builders and subcontractors who provide faulty
housing. This is true today for houses built on slabs, basements,
or wall-vented crawlspaces. There are several alternative
approaches to maintain these systems. For example, some
forward-thinking pest control operators are installing dehumidifiers in closed crawlspaces and including equipment service
during their annual crawlspace inspection for termites. Other
manufacturers have liquid water alarms to install in crawlspaces. Closed crawlspace construction is not a magic, silver
bullet that will solve all construction wrongs. Its practical
construction methods must also be properly applied.
Initial information from contractors who are providing
closed crawlspace systems to general contractors for new
construction has found packages priced from $1.50 to $3.50/ft2
for a range of installations. These sample installation costs do
not take into account the cost reductions that the builder will
realize from not installing certain other features that are
replaced by the different closed crawlspace systems. Initial
construction costs associated with building closed crawlspaces
will almost always be more than for traditional wall-vented
construction. As the new construction methods are evaluated
both by builders and researchers, it will be important to factor
in the value of reduced callbacks for moisture and mold
complaints; the perception of enhanced value by the consumer
and resulting improvement in sales price and volume; and
reduced legal exposure. Reduced maintenance, a reduction in
costly, long-term repairs, and significant energy savings will
enhance the value of closed crawlspace construction to the
consumer. The future could include insurance premium savings
for houses built on certified closed crawlspaces.
9
RECOMMENDATIONS
There is a need to make building codes accommodate and
provide for closed crawlspace construction. During our work to
set up the houses in this study, the scattered and conflicting
nature of different elements within the building code became
evident. For closed crawlspaces to be practical for both builders
and code enforcement officials, we are recommending a separate section in the code that is specifically dedicated to these
construction methods. We have created that draft code language
for a separate section. As long as closed crawlspace construction is presented as a fragmented set of exceptions in the code
for traditional wall-vented crawl spaces, it will be subject to
varying interpretations by code bodies unfamiliar with and
uncertain about these closed crawlspace construction techniques.
Properly closed crawlspace strategies must address the
following design issues: (1) pest management, (2) moisture
management, (3) fire safety standards, (4) thermal standards, (5)
combustion safety, and (6) radon management. Successful
implementation strategies will require attention to the following
construction management issues: (1) understanding crawlspaces as physics- and logic-free zones (people have beliefs
about crawlspaces rather than knowledge) and the necessity of
beginning discussions with that in mind; (2) selection of a
closed crawlspace system; (3) pricing closed crawlspace work;
(4) managing labor (confined space safety, hard work, job skills,
pay); (5) managing job site logistics; and (6) applying and
adjusting codes and working with code officials. Closed crawlspace construction is a very effective measure, but it is not a
magic bullet. One can inadequately apply closed crawlspace
details and sequences as easily as any other construction
component. Installers have to responsibly plan and deliver the
work to achieve the total package of benefits.
CONCLUSIONS
Closed crawlspace construction techniques are robust
measures in the hostile southeastern humid climate for providing dry crawlspaces for new construction and for retrofitting
existing houses. These crawlspaces have a sealed polyethylene
film liner system to reduce moisture intrusion from the soil and
the masonry walls and from outside air flow into the space. They
require that both ground and surface water be prevented from
entering the crawlspace. They also require some type of supplemental drying mechanism to control the limited amount of
moisture vapor that will still migrate to the space and would
accumulate over time. Phase I of this study has demonstrated
that a measured amount of duct air leakage would provide that
control. However, we are not advocating duct leakage as a standard moisture control strategy. For a temporary period during
Phase I, the study also demonstrated that small dehumidifiers
would easily provide even greater control for crawlspace relative humidity. Phase II has demonstrated that a measured
amount of HVAC supply air (1 ft3/min [0.5 L/s] for each 30 ft2
[2.8 m2] of crawlspace ground surface) also provided the necessary supplemental moisture vapor control. Other supplemental
drying mechanisms have not yet been evaluated. Closed crawlspace construction produced an environment that slowed down
10
and reduced the extremes of the moisture and temperature
swings that were experienced in wall-vented crawlspaces.
Closed crawlspace experiment groups one and two maintained air relative humidity below 60% and dew-point temperature below 60°F (16°C). Wall-vented crawlspaces maintained
extended periods of time with air relative humidity above 80%
and dew-point temperature in the mid-seventies (21°C). In addition they experienced periodic episodes of dew-point condensation. These conditions resulted in microclimatic conditions
that supported mold growth and moisture deterioration of materials and equipment located in these types of crawlspaces.
Insulation in closed crawlspaces in the southeastern United
States has been demonstrated to be effective when fiberglass
batts were applied in the floor cavity. It has also been effective
when foam board was applied against the inside of the foundation wall. These two approaches have different performance
characteristics for the different seasons. On an annual basis they
both outperform conventional crawlspace construction methods with a 15% reduction in space conditioning energy used.
This magnitude of space conditioning energy savings was unexpected and when combined with the moisture benefits of closed
crawlspaces bolsters the argument for adoption of closed crawlspaces in the construction industry. Future study is necessary to
determine how well these results will transfer to other houses
with different geometry and located in different climates.
However, several production builders and some product manufacturers are already benefiting by promoting dry crawlspace
construction techniques, and this segment of the construction
industry is poised for substantial growth. The widespread application of these construction methods where it is determined to
be appropriate will benefit homeowners, construction businesses, energy policy, and the environment.
ACKNOWLEDGMENTS
This investigation is co-funded by Advanced Energy and
the U.S. Department of Energy, National Energy Technology
Laboratory, Cooperative Agreement Instrument #DE-FC2600NT40995.
REFERENCES
ASHRAE. Recommended Practices for Controlling Moisture
in Crawl Spaces, ASHRAE Technical Data Bulletin, volume 10, number 3.
Davis, B., W.E. Warren, and W.B. Rose. 2002. Technology
Assessment Report. A field study comparison of the
energy and moisture performance characteristics of ventilated versus sealed crawl spaces in the south. Advanced
Energy, Raleigh, NC.
Rose, W. B. 1994. A review of the regulatory and technical literature related to crawl space moisture control. ASHRAE
Transactions 100(1). Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers.
Rose, W.B., and A. TenWolde. 1994. Issues in crawl space
design and construction— A symposium summary. Recommended Practices for Controlling Moisture in Crawl
Spaces, ASHRAE Technical Data Bulletin, volume 10,
number 3. <www.ashrae.org>.
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